This PR makes platform views ignore pointer events when they're not laid
out.
Platform views register themselves for global pointer events when their
RenderBox attaches:
9c626d9f9a/packages/flutter/lib/src/rendering/platform_view.dart (L370-L380)
But a RenderBox that is attached is not necessarily laid out. The
problem in the issue seemed to be that a page was created offscreen
(attached and not laid out), but it still received pointer events, and
this caused errors with using `size` before layout.
This PR simply ignores pointer events when not laid out.
Fixes https://github.com/flutter/flutter/issues/83481
e244168327